1. Field of the Invention
This invention relates to a method of the surface treatment of a porous material.
2. Prior Art
In the remainder of the description, the term "porous material" denotes a porous metal material or a material having a porous metal surface.
Conventionally, the pores of a porous material, such as aluminium having an anodic oxide film or a sintered alloy, are filled or impregnated with a solid lubricant such as powder of molybdenum disulfide, powder of tungsten disulfide powder of polyfluoroethylene or colloidal carbon to lower a coefficient of friction of the surface to improve lubricating properties thereof. The porous material so treated is used as machine component parts, which require high wear resistance, such as a bearing member. One method of filling the solid lubricant is known in which the porous material is immersed in a solid lubricant in the form of powder. Another filling method is also known in which a powder lubricant is dispersed in a liquid to provide a dispersion in which the porous material is immersed. These filling methods have been found not satisfactory in that the powder lubricant fails to be adequately filled in the pores of the porous material in the case where the pores do not have an adequate size or have a complicated shape. For example, the diameter of the micropores of the anodic oxide film of aluminum is very small and is on the order of 100 to 500 A, and it is almost impossible to fully fill the micropores with a powder lubricant of molybdenum disulfide. In addition, the micropores have a depth of 10 to 200.mu. which is greater in comparison with its diameter, and therefore the powder lubricant can be filled only in that portion of each micropores near its opening. This is undesirable in that the porous material so treated, when used as a wear resistant material, can not maintain required wear resistant properties for a prolonged period of time.